five feet long by a foot or so in width at the mouth, with a scraper like a narrow hoe on one side, and a suspending apparatus attached to the rope on the other. From the frame is suspended a bag, about two feet in depth, of wide netting or hempen cord. The naturalists' dredge has a scraper on each side, the bag is deeper, and the meshes so fine as to allow only the water to pass through.
Fig. 5 represents the dredge devised by Dr. Ball, of Dublin, and which scraped the surface so perfectly that, when drawn along a drawing-room floor, it would pick up the pence that had been scattered before it. Dr. Thomson states that the most convenient size for